In the case where a substrate, provided with an RF circuit, is connected to a waveguide, there arise problems that reflection, transmission loss, and leakage of an electromagnetic wave are increased, and various connection structures have been proposed for solving the problem.
Patent literature 1 (hereinafter “PTL1”) discloses a connection structure connecting a dielectric substrate, on the surface of which a signal transmission line is formed, to a waveguide via an insulating connection member which is provided with a through hole having the same size as the inner diameter of the waveguide. Also patent literature 2 (hereinafter “PTL2”) discloses a structure connecting a high frequency module to a waveguide substrate via a dielectric substrate and proposes a structure in which electromagnetic wave leakage is suppressed by means of providing a choke groove around a waveguide hole of the waveguide substrate and further providing a land around a through hole having the same size as the waveguide hole of the dielectric substrate.